Two years after the end of Kamen Rider the First, a strange series of murders occur with people dying in a most gruesome fashion with a song played by pop star Chiharu playing at the site of the murder. Meanwhile, Takeshi Hongo has become a high school science teacher. A student in Takeshi's class named Kotomi Kikuma is best friends with Chiharu and is worried about her since her disappearance. Then a mysterious woman, known as the Chainsaw Lizard, appears alongside six new Riders known as the Shocker Riders.

Chiharu has a brother named Shirō Kazami, who is president of the rising IT enterprise ExaStream. Takeshi and Kotomi investigate Kazami, but soon discover that Shocker have used nano-technology to turn Kazami into a cyborg code-named "V3". V3 and the Shocker Riders attack Takeshi, forcing him to become Kamen Rider 1 once again. Kamen Rider 2 then re-appears to aid Kamen Rider 1 once more. Scissors Jaguar, another Shocker creation, begins a plan to convert all the humans in Japan into cyborgs using nanobots that will infest Japan. The three Riders put aside their differences to fight Shocker together and save Chiharu, who is the victim of the very nano-technology. ( source from wikipedia)